This invention relates generally to devices, systems, and methods for combustion, including but not limited to devices, systems, and methods for generating steam for example for use in hydrocarbon production, and in particular, enhanced production of heavy hydrocarbons from subsurface hydrocarbon formations.
Development of oil fields generally occurs in three stages. The first stage of oil field development is primary recovery. During primary recovery, one or more holes are drilled from the surface down into the hydrocarbon reservoir. The pressure present in the underground hydrocarbon reservoir forces hydrocarbons through the wellbore to the surface. Primary recovery continues until the pressure in the hydrocarbon reservoir is insufficient to force hydrocarbons through the wellbore to the surface. Typically only 5 percent to 15 percent of the original oil in the reservoir can be recovered during the primary recovery stage.
The second stage of oil field development is secondary recovery. During secondary recovery, various techniques may be used to recover hydrocarbons from reservoirs with depleted pressure. One technique, known as reservoir flooding, involves injecting fluids, such as water, to increase reservoir pressure in order to force hydrocarbons through the wellbore to the surface. An alternative technique, known as gas lift, involves injecting gases, such as carbon dioxide, to reduce the overall density of fluid in the wellbore. The formation pressure is then sufficient to force the less-dense fluid through the wellbore. Sometimes, pumps may be used to extract oil to the surface from the hydrocarbon reservoir. Typically, only 20 percent to 40 percent of a reservoir's original oil can be extracted by primary and secondary recovery.
The third stage of oil field development is tertiary recovery, also known as enhanced oil recovery (EOR). Following secondary recovery, a large percentage of hydrocarbons remain trapped in the reservoir. During EOR, various methods are used to increase the mobility of the oil in order to increase extraction. The most common method of EOR is steam injection. Typically, steam is produced using a steam generator at the surface, often part of a cogeneration plant. The steam then is injected into the reservoir through a wellbore where it heats the oil, thereby reducing its viscosity and making it easier to extract. Current steam-based oil recovery methods are effective only to about 2,500 feet due to heat and pressure losses. Surface steam production also undesirably generates substantial greenhouse gas emissions.
An alternative EOR method is carbon dioxide flooding, in which carbon dioxide is injected into an oil reservoir where it mixes with the oil, reducing its viscosity and making it easier to extract. Carbon dioxide flooding is particularly effective in reservoirs deeper than 2,000 feet where carbon dioxide is in a supercritical state. Other alternative EOR methods include injecting fluids that reduce viscosity and improve flow into the hydrocarbon reservoir. These fluids may include gases that are miscible with oil, air, oxygen, polymer solutions, gels, surfactant-polymer formulations, alkaline-surfactant-polymer formulations, or microorganism formulations. Current methods of EOR typically allow only an additional 5 percent to 15 percent of a reservoir's oil to be recovered.
The amount of hydrocarbons that are recoverable is determined by a number of factors including the depth of the reservoir, the permeability of the rock, and the strength of natural drives, such gas pressure, pressure from adjacent water, or gravity. One significant factor is the viscosity of the hydrocarbons in the reservoir. The viscosity of hydrocarbons ranges extensively from light to heavy. Lighter oils typically result in higher extraction rates. On the other hand, heavy oil, bitumen, and methane hydrate are highly viscous or solid and almost impossible to extract using conventional oil production methods. Heavy oil is typically classified as oil having an API gravity of about 10 to about 20 and a viscosity greater than about 100 cP. Bitumen is a semi-solid or solid hydrocarbon substance that typically has an API of less than about 10 and a viscosity of greater than about 10,000 cP. Methane hydrate is a solid form of methane trapped within a crystal structure of water. Heating methane hydrate can release gaseous methane from its crystal lattice structure.
Heavy oil and bitumen reserves below 2,500 feet onshore and at all depths offshore cannot be produced using current steam technology. According to a National Institute for Petroleum and Energy Research (NIPER) study, more than half of the 68 billion barrels of remaining heavy oil reserves in the United States are below 2,500 feet. A Technical, Economic, and Legal Assessment of North American Heavy Oil, Oil Sands, and Oil Shale Resources, U.S. Department of Energy, http://fossil.energy.gov/programs/oilgas/publications/oilshale/HeavyOilLowRes.pdf. If half of the heavy oil and oil sand deposits in the United States and Canada were brought to market, they alone could satisfy the current demand for crude oil in both countries for more than 150 years. America's Oil Shale: A Roadmap for Federal Decision Making, U.S. Department of Energy, http://fossil.energy.gov/programs/reserves/npr/publications/oil_shale_roadmap.pdf.
Accordingly, it would be highly desirable to provide devices, systems, and methods for enhanced production of hydrocarbons from subsurface hydrocarbon formations. It would be particularly desirable to provide devices, systems, and methods for extraction of heavy oil, bitumen, and/or methane hydrate deposits, especially at depths greater than 2,500 feet.
U.S. Pat. Nos. 4,604,988 and 7,780,152 disclose efforts to solve this problem by providing a downhole steam generator. However, improvements are needed to provide combustion devices that are more efficient, reliable, and/or durable in long-term continuous use.